1. Field of the Invention
Embodiments of the present invention relate generally to charging uninterruptable power supply batteries. More specifically, at least one embodiment relates to non-isolated chargers with bi-polar inputs.
2. Discussion of the Related Art
Uninterruptible power supplies (UPS) are used to provide reliable power to many different types of electronic equipment. Often, this electronic equipment requires particular voltage and/or current input from a UPS. Unintended fluctuations in UPS power output can damage electrical equipment, which results in a loss of productivity and can require costly repair or replacement of electrical components.
FIG. 1 provides a block diagram of a typical on-line UPS 100 that provides regulated power as well as back-up power to a load 140. UPS's similar to that shown in FIG. 1 are available from American Power Conversion (APC) Corporation of West Kingston, R.I. The UPS 100 includes a rectifier/boost converter 110, an inverter 120, a controller 130, a battery 150, and an isolation transformer charger 160. The UPS has inputs 112 and 114 to couple respectively to line and neutral of an input AC power source and has outputs 116 and 118 to provide an output line and neutral to the load 140.
In line mode of operation, under control of controller 130, the rectifier 110 receives the input AC voltage and provides positive and negative output DC voltages at output lines 121 and 122 with respect to a common line 124. Isolation transformer charger 160 can be employed to charge battery 150 using an isolation transformer. In battery mode of operation, upon loss of input AC power, the rectifier 110 generates the DC voltages from the battery 150. The common line 124 may be coupled to the input neutral 114 and the output neutral 118 to provide a continuous neutral through the UPS 100. The inverter 120 receives the DC voltages from the rectifier 110 and provides an output AC voltage at lines 116 and 118.
Existing schemes for charging UPS batteries employ an isolated half-bridge topology including a relatively large isolation transformer that is costly, requires a plurality of highly rated associated components, and can saturate due to flux to imbalance, causing semiconductor device failure.